The following test program

static int vector_to_bit(int vector)
{
  return 1U << (vector & 0x1fU);
}
static volatile int *vector_to_imr(int vector)
{
  return (volatile int *)(vector + 64);
}
void bsp_interrupt_vector_disable(int vector)
{
  volatile int *imr = vector_to_imr(vector);
  int bit = vector_to_bit(vector);
  *imr |= bit;
}

yields

m68k-rtems4.12-gcc -S -mcfv4e -O2 test.c -o /dev/null
test.c: In function 'bsp_interrupt_vector_disable':
test.c:14:1: internal compiler error: in find_reloads, at reload.c:4077
 }
 ^
0x7f2c13 find_reloads(rtx_insn*, int, int, int, short*)
        /home/EB/sebastian_h/archive/gcc-git/gcc/reload.c:4077
0x80037d calculate_needs_all_insns
        /home/EB/sebastian_h/archive/gcc-git/gcc/reload1.c:1472
0x80037d reload(rtx_insn*, int)
        /home/EB/sebastian_h/archive/gcc-git/gcc/reload1.c:987
0x6e798c do_reload
        /home/EB/sebastian_h/archive/gcc-git/gcc/ira.c:5484
0x6e798c execute
        /home/EB/sebastian_h/archive/gcc-git/gcc/ira.c:5656
Please submit a full bug report,
with preprocessed source if appropriate.
Please include the complete backtrace with any bug report.
See <https://gcc.gnu.org/bugs/> for instructions.